This invention relates to a single or multistory modular compound composite concrete and steel floor for modular buildings. The objective is not only to provide an economical, structurally efficient, higher quality and more durable modular building, but to be able to handle, transport and install it economically as well.
Theoretically, an item built in mass production in a controlled environment ought to be able to be produced at a lower cost and higher quality than the same item built on a custom basis out in the elements. This is experienced in the auto industry, the computer industry and many others. This has not, however, been experienced as successfully in the building construction industry. It is true that structural members, plumbing, mechanical, electrical and other building components have adopted mass production, but their complete assembly into a building has not. The bulkiness of buildings generally does not allow them in whole to be built in a factory or easily shipped and installed. As a result, buildings were divided into sections or modules, mass production was attempted to be applied and the modular building process was created. But even this industry has not achieved the economical and quality benefits the production process ought to provide. In most areas of the country commercial modular buildings are generally no less expensive than a building built on site. And the durability, quality and aesthetics of the modular product often does not match that of conventional. So if value is the measure of quality versus cost, unlike other industries, the modular production process has provided less value than conventional construction. As a result the modular industry has managed to capture only a relatively small part of the construction market. Namely, that part of the market that must be relocatable. If a commercial building can be built conventionally, modular generally has not been considered an option. Reasons for the inability of the industry to provide more value than conventional construction include: shipping restrictions, architectural paradigms and quality gaps, shipping and handling costs and, apparently, a lack of expertise to overcome these characteristics.
The most obvious characteristic of modular construction is that the modules must be transportable. This poses challenges in several ways. Transportability is mainly a function of road and bridge geometry and strength. As a result, modules have to fit within maximum rectangular volume and weight constraints regulated by the department of transportation or some other governmental agency. Roads in the US have relatively liberal widths but other factors such as telephone poles and signs on street corners make it difficult in some cases to maneuver wide or very long modules. But this is much less of a problem than the height limitations imposed by bridges, power lines, trees and other obstacles.
In addition, over the long history of building construction has evolved distinct architectural, safety and non discriminatory building paradigms. In the more populated areas and therefore major market areas, the market has demanded and even empowered local governments to create building ordinances to ensure some or all of these paradigms are adhered to. The more basic ones include, for example, high pitched roofs in residential areas, high ceilings in all construction, fire resistive construction and minimum requirements for egress and handicap access in commercial construction. And in recent years, local planning ordinances require minimum percentages of masonry on the exterior facade. These paradigms, desirable or mandatory, again pose challenges to the modular production process. Shipping height restrictions limit the height of roofs and the use of high or cathedral ceilings. Fire resistive materials tend to increase weight. In the past, in order to minimize weight, modular buildings have been built of wood products. However, because wood is combustible, building codes restrict the size of wood buildings and require fire rating and sprinkler systems when the floor area reaches a certain size. Wood is subject to termites and rot and is a relatively weak material whose strength diminishes when it gets wet. In areas where basements are generally not used, the lowest portion of the typical wood framed floor structure is required to be set a minimum of a half of a meter above grade so that moisture cannot cause it to deteriorate so quickly. This necessitates skirting the exterior walls to the ground, steps at all doors and a handicap ramp at least at one main door. These are large expenses if constructed of the more accepted poured on site concrete with steel handrails and relatively expensive and unappealing if constructed of the typical pressure treated wood. And finally masonry materials are very heavy and almost all but thin veneers such as stucco are almost impossible to attach to the building for shipping.
Also, as with any other manufactured product there are shipping, handling and installation costs. Although it is true materials have to be shipped to the conventional site, there is a well established infrastructure and materials have to delivered to the modular plant, as well. Shipping the modules is above and beyond this. And of course, the cost is proportional to size, weight, distance and quantity. The largest modules require escorts in addition to the equipment to pull it. Heavier modules require larger or stronger equipment to pull and handle them. Trucking company""s charge by the mile and of course this is multiplied by the number of modules there are. Installation cost is a function of the number of modules. And material has to be applied to protect the modules from the elements until they are installed.
Further, shipping and handling a module can require applying forces on it in different locations or in larger magnitudes than would be experienced in the installed position on the foundation. Therefore, packaging not only includes protecting the product from the elements, but providing the appropriate structure or mechanism to withstand the stresses, deflections, vibrations and impacts induced by handling and the dynamics of traveling down the road. None of which may be experienced in conventional construction. These loads have been supported in an array of ways by the addition of columns, beams and braces in some manner or another. Since bending resistance is proportional to the cross sectional height of a member to the third power, the taller the beam the less it has to weigh and the more economical it will be. As height is one of a modules most valuable commodities, the tendency is to compress structural member height as much as possible. This has made it a challenge to incorporate strong efficient economical modules and packaging structures. The inverse of the beam strength characteristic is; to maintain strength, for very small reductions in height you have to add a lot of weight. As a result, short heavy inefficient members have been used. Resolving this issue would contribute the majority of the solutions to most of the other challenges as well. This requires a design that makes height restricted beams their most efficient. The solution lies in distributing as much of the cross sectional area that makes up the beam to the very top or bottom of the beam height limitations, as possible, and using the most suitable material in those top and bottom flanges.
In summary, all of these challenges contribute significant costs to a modular building that a conventionally built building would not have. But, they cannot be completely eliminated because a modular building has to be shipped. However, a properly designed system and production process should generate economic benefits that far outweigh the costs of shipping and installation, while providing the quality demanded by architectural paradigms. Only when costs and quality meet or exceed that of conventional construction can market share increase. This can only be accomplished by designing the most efficient structure and utilizing or exploiting some of conventional construction""s inherent characteristics or weaknesses as well. This requires; shipping the largest module that can travel through the restriction envelope, providing a product that; is more appealing and acceptable to the market and local planning commissions, is more durable, is safer and minimizes additional on site work, minimizing weight, reducing structural redundancies for shipping, providing multistory modules to capitalize on the inefficiency of conventional construction on upper stories and utilizing conventional finishes where it is the optimal process.
I have worked in the modular building industry since 1987. And although the industry employs architects and professional engineers, the challenges listed above have continued to deter the industry from providing an economical system that can compete with the cost and quality of site built construction. Much headway wasn""t made until 1996 when I developed and built an economical modular reinforced concrete floor for a previous employer. However, there didn""t appear to be enough support in implementing the new product before it became common knowledge. Rather than continue with them, in 1997 I resigned and began working on a new design. Unlike the previous design, the present invention not only concentrates on an economical floor, but is lighter, stronger, can be used in multistory applications and emphasizes transportability and ease of handling as well. By incorporating the concept of a composite xe2x80x9cTxe2x80x9d beam which can be attached to other structural elements to create a compound and composite floor structure, optimal efficiency can be achieved. The final assembly being much stronger than the sum of the strength of the parts.
In reviewing the prior art, I believe the concept of applying composite xe2x80x9cTxe2x80x9d beam designs to modular building floor structures to be new. In the past, in the market, when concrete floors were required, with few exceptions, the strength was accomplished by utilizing large heavy steel members alone without incorporating the concrete floor into a composite beam or the concrete floor and other elements together as a compound composite beam. These heavy beamed systems are expensive and unable to compete with site built construction. In addition, the concept of creating a compound composite xe2x80x9cTxe2x80x9d beam by attaching the floor to a lighter carrier or first story ceiling frame, to my knowledge, has never been considered.
Several precast concrete manufacturers produce prestressed double xe2x80x9cTxe2x80x9d panels for conventional construction. However, these panels are extremely heavy and not suitable for modular buildings or attachment to a carrier for transporting the floor and the remainder of the building module""s components such as walls, ceilings, roofs and subsystems etc. from the plant to the job site.
Design calculations for the present invention were based on engineering theory assimilated basically from the inventor""s engineering education and from Hick""s, Standard Handbook of Engineering Calculations, published in 1972 by McGraw Hill. This reference discusses theory and calculations for several design methods for compound, composite and xe2x80x9cTxe2x80x9d beams separately, but does not specifically discuss or provide a design method for the subject invention or any other modular concrete floor.
Previous patents have made attempts to resolve some of the challenges of modular construction, but very few provide the comprehensive solution the present invention does. A lot of them are penalized wall systems. Others are variations of existing structurally inefficient modules or some part thereof Some take a residential perspective and others a commercial, but any found to address one or more of the challenges listed above are discussed here. To start, U.S. Pat. No. 5,765,316 to Kavarsky (1998) attempts to solve the shipping height and pitched roofs problem with a telescoping members and a hinged roof This requires some relatively expensive column and hinging devices and then a lot of finishing on site.
The following patents attempt to address fire resistance, strength and durability with versions of steel and/or concrete modules. These are typically single story only, structurally inefficient and/or heavy and therefore not cost competitive, but worthy of mention because they typify the general nature of the modular industry. U.S. Pat. No. 4,882,883 to Horn (1989) is closest to the typical lightweight steel framed module built today. The floor is a welded steel main frame and joist with an expensive metal deck welded on top which is then covered with a wood floor deck. The floor structure tends to deflect during transportation if additional bracing is not installed and may cause the floors to have high and low spots. In addition, the floor system sounds hollow when you walked on it giving it the impression of a mobile home. And typically, if the customer accepted the mobile home feel there were plenty of wood framed modular systems that were more economical than this structure. Further, it is believed these are still set off the ground like a mobile home which required the use of skirting and steps and ramps at the entrances. U.S. Pat. No. 4,833,841 to Ellington (1989) has a steel mainframe that supports a concrete floor in a metal composite deck. The author of the present invention actually went to work for this company in 1987 and 1988 after it was developed. At the time this appeared to be a good system. However, in the last few years the author has strengthened his structural knowledge and now sees the deficiencies of this system as well. The floor slab was very heavy and inefficient which did not allow the modules to maximize the allowable shipping volume. U.S. Pat. No. 5,113,625 to Davis (1992) shows a floor that requires a xe2x80x9cpanxe2x80x9d on top and between main beams and steel joists to support insulation. A relatively expensive corrugated metal deck is required to be welded on top of the steel framing and then concrete is poured in which is reinforced with some unidentified reinforcement. But then in contrary to the reinforcement and a desire to xe2x80x9cwithstand high stress loadsxe2x80x9d joints are formed into the concrete with xe2x80x9csplittersxe2x80x9d to prevent cracking. U. S. Pat. No. 5,044,134 to Brockway (1991)is a steel structure. The floor and walls are framed and sheathed with steel and the module is then shown to be placed on a slab poured on site. This has redundant floor structures and probably would not be an energy efficient structure for residential or commercial use. U.S. Pat. No. 4,910,932 to Honigman (1990) is actually concrete and steel wall and floor panalized system, where the panels are produced in a plant, trucked in a flat stacked manner and then assembled on site. But as with the xe2x80x9csplittersxe2x80x9d above, a lot of joints in a structure do not tend to induce strength and structural or energy efficiency, not to mention aesthetics.
Several patents attempt to address durability and fire resistance in different versions of multistory modules. This is a step in the right direction because manufacturing a module on the ground and then setting it in place should be safer, faster and more efficient than having to maneuver labor, equipment and materials up and down 2 or more stories in a conventional manner. These come in two varieties; completely concrete or steel frame and concrete.
In the completely concrete group, U.S. Pat. No. 4,930,273 to Papesch (1990) actually appears to only address a stair system and ingress egress flow for a multistory modular concrete building. U.S. Pat. No. 4,525,975 to McWethy (1985) illustrates a multistory modular building where the concrete modules, each with four walls and a floor, are set apart from each other slightly. The cavity created between the outside walls of two adjacent modules is reinforced and more concrete is poured in between. These are very heavy and cannot be built in large pieces. U.S. Pat. No. 3,952,465 to Masiello (1976), 5,233,808 to Salmenmaki et al. (1993) and 3,992,848 to Stucky (1976) again are modules with relatively thick, heavy concrete floors and walls, but do not require pouring additional concrete for the structure. These patents typically don""t detail how utilities are installed or how the walls are insulated and may require additional material and labor to provide chases for these items.
In the, lighter, steel frame and concrete floor group; U.S. Pat. No. 4,513,545 to Hopkins, Jr. (1985) is a multistory framed modular system that requires a slab be poured on site for the first floor and then uses a framed floor for subsequent stories. U.S. Pat. No. 4,807,407 to Horn (1989) is a steel framed module that describes a system for lifting it with a crane and has the floor system shown in U.S. Pat. No. 4,882,883 to Horn (1989). This illustrates some of the redundant members that have been used to aid in shipping and handling. The author is not sure if U.S. Pat. No. 4,077,170 to van der Lely (1978) is meant to be a multistory system or not, but placed it here because it is the next step in a series of better designs than have been discussed so far. It has a clever floor structure where the steel frame has welded to its top flanges a grid of reinforcing bars. The floor structure is turned over and immersed into an approx. 5 cm thick bed of concrete, allowed to harden and then flipped back over. This appears to be the most efficient structure thus far, however, with a few corrections it could be much better. To start, the slab and the main frame beams may separate and or be subject to sliding relative to each other under load. Another element may need to be added to prevent this and make the system much stronger. Also, it appears that the slab could develop cracks above the beams that support it due to a lack of reinforcement against the negative moments that would develop, especially over a member like intermediate beam 7 in FIG. 15. This would render the slab in effect a series of simple beams that would be subject to larger stresses and deflections than a multispan configuration would. In addition, members 141 are not in the optimal location. And finally, having to flip the steel frame and then the steel and concrete floor may be a capital intensive process. U.S. Pat. No. 4,545,159 to Rizk (1985) has many features that make it the best, in the authors opinion, of the prior art. It has an approx. 5 cm thick slab also, but it improves on some of the deficiencies of the previous patent. First it utilizes shear connectors to tie the slab to the main frame. This helps to make a much stronger member. Second, it ties the intermediate framing into the slab as well. Third, it shows a wire mesh that is not required to be welded to the steel frame for reinforcing as opposed to the more labor intensive individual reinforcing bars. Some of the criticisms, though, would include, again a possible lack of negative reinforcement. The use of a bar joist for the main frame is a good idea in upper stories, but causes the first floor to sit above grade, necessitating skirting, steps and ramps. Also the bar joist is shown in a simply supported situation and there is redundant framing in the ceiling not connected to the light bar joist above. This is not the most efficient framing system and even though the bar joist is tied into the slab, the spanning capabilities of this structure appears to be minimal. Also, as with the previous patent, the main frame members are placed on the perimeter of the concrete slab creating an upside down double xe2x80x9cLxe2x80x9d shaped beam. The standards regulating the concrete and steel industries don""t allow the strength that a xe2x80x9cTxe2x80x9d beam can provide if the top flange does not overhang either side of the web a minimum amount. In addition, the main frames on the perimeter cause the transverse purlins to act as simply supported members. This is not the most efficient beam configuration. Further, the exterior finish appears to be complicated and industrial looking. This is not appealing today with the popularity of modern neo-classical architecture. And finally, as with the previous inventions, transportation and handling is not detailed and could be difficult.
U.S. Pat. Nos. 4,065,892 and 4,067,158 both to Lawrence (1978) attempt to address transportation by utilizing a reusable axle and hitch assembly. As shown in U.S. Pat. No. 4,114,328 also to Lawrence (1978) from the perspective of a wood framed module requires that it be rigid enough to span the distance from the hitch to the set of axles. This is an efficient transportation system if this is the case. However, there are many building situations where there are no or too few walls or the correct structure to provide the necessary rigidity. And the typical wood framed floor structure could not span this distance without them. In this case, additional temporary bracing is required and if steel beams are still required below the wood framing than this is less efficient than just using the steel beams alone.
The aforementioned patents attempt to solve some of the challenges associated with modular construction. Some maybe good ideas and others not so good, but none of them provide an all encompassing optimum solution. The present invention provides a building system with a more comprehensive more efficient solution than has been provided in the prior art.
Objects and Advantages
Several objects and advantages of the present invention are:
(a) to provide a multistory modular compound composite concrete and steel floor that can be produced for about the same cost that standard modular wood floors are produced today;
(b) to provide a multistory modular compound composite concrete and steel floor that can be as easily and economically transported, installed and relocated as modular wood floors;
(c) to provide a multistory modular compound composite concrete and steel floor that can be produced more economically than existing modular concrete floors;
(d) to provide a multistory modular compound composite concrete and steel floor that can be more economically transported, installed and relocated than existing modular concrete floors;
(e) to provide a multistory modular compound composite concrete and steel floor building system that can compete with, if not outperform, conventional construction in cost, quality and aesthetics.
Still further objects and advantages will become apparent from consideration of the ensuing drawings and description.